1. Field of the Invention
The present invention relates to a photo-sensitive flexographic printing plate composition imparting a soft printing plate by rubber compounding photosensitive resin.
2. Related Art Statement
Hitherto, as a flexographic printing plate, use is mainly made of a rubber plate, and such rubber plate is manufactured through a complicated process such as a process for forming a metallic original plate by etching a metal plate, a process for forming a matrix by heat pressing the metallic original plate to thermosetting resin, a process for forming a vulcanized rubber sheet by hot pressing a rubber sheet to the matrix and the like. However, such a process has many disadvantages such as poor reproducibility of a fine image portion owing to repetitive image decal, waste of cost and time owing to requirement of many processes, necessity of skilled workers, defaced dots at the time of printing and the like.
Moreover, fine image printing is difficult, and a viscosity of the obtained rubber plate itself is low, so that there are such disadvantages that back shaving is required in use, manufacturable printing plate size is limited in apparatus and process, and any big size cannot be obtained.
In order to solve the above disadvantages, it is common practice today to directly manufacture a printing plate with the use of a photosensitive resin composition.
As such a printing plate composition, use is made of urethane modified acrylate obtained by introducing polyether or polyester into a compound having a polymerizable double bond, a Styrene-butadiene block copolymer, a Styrene-isoprene block copolymer, 1,2-polybutadiene and the like, and they satisfy the usually required hardness (Shore hardness A 40-80), but are insufficient in toughness, so that a printing plate and its relief are broken, a relief depth is shallow, and a moldable hardness range is narrow.
In order to improve performances of these relief plates, there have recently been developed widely usable rubbers such as chloroprene rubber, acrylonitrile-butadiene rubber, Styrene-butadiene rubber and the like, a photosensitive resin composition consisting essentially of a photopolymerizable monomer and a photopolymerization initiator.
However, a printing plate with the use of prior photosensitive resin generally becomes a highly hard rubber plate, lacks rubber elasticity, and is poor in transition against durability, solvent resistance, wear resistance and aqueous ink as compared with a vulcanized rubber printing plate. Moreover, even in case of using a low hardness rubber plate, there is no rubber elasticity and restorability for printing is lowered.
Moreover, in case of a resolution film-casting drying method with the use of a solvent, a process for removing the solvent is required, the process becomes complicated, a thick article is difficult to be manufactured, a plate is liable to be strained, and change in quality easily occurs at the time of drying.
Particularly in flexographic printing on a printing body of coarse material and a printing body having uneven thickness, plate making is complicated, and at present a photosensitive printing plate composition having satisfiable performance cannot yet be obtained.